CN102660967B - Method for determining cold region single-pile experiential rheology prediction equation - Google Patents
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Abstract
The invention discloses a method for determining a cold region single-pile experiential rheology prediction equation. The method comprises the following steps of: acquiring water content and earth temperature data of a soil sample of a pile foundation construction area; finding the corresponding coefficients of the rheology prediction equation in an experiential rheology prediction equation coefficient list obtained by test data regression analysis according to the water content and earth ground data and pile body materials; and determining the cold region single-pile experiential rheology prediction equation according to the coefficients of the rheology prediction equation. By the nonlinear fitting of measured data of single pile top displacement, pile end displacement and pile end stress, and the balance principle of force, the uniform expression form of the rheology equation of the single pile top displacement, the pipe end displacement, the pile end stress and pile side average freezing stress can be obtained, the single-pile rheological effect is predicted, and the aims of simplifying the design process of a frozen soil pile foundation and reducing design cost can be fulfilled.
Description
Technical Field
The invention relates to the field of frozen soil vertical piles in cold regions, in particular to a method for determining a single-pile rheological prediction equation in single-pile design of a building pile foundation on frozen soil in cold regions.
Background
China is the third frozen-soil country in the world after russia and canada, and the frozen-soil area accounts for about 75% of the national soil area. The Qinghai-Tibet plateau is a perennial frozen soil area of the plateau with the largest permafrost distribution area and the highest altitude in the world. The frozen soil is rich in ice crystals, and stress concentration occurs at the contact point of solid particles under the action of external pressure and temperature load, so that the frozen soil is a material medium with obvious rheological properties due to the characteristics of viscoplastic flow of ice on one hand, melting of ice and water migration on the other hand. The rheological properties of frozen earth directly influence the mechanical properties of the pile. The deformation and stress of the frozen soil change along with the change of time, and the displacement and stress of the pile change along with the change of time as a result, so that the consideration of the rheological property of the foundation soil in the analysis of the pile foundation is the inevitable requirement for designing the pile foundation safely and reasonably.
The bearing capacity of the cold region frozen soil pile foundation is a key parameter in pile foundation design, and the rheological property of the pile foundation must be considered in calculation. At present, the rheological effect of a single pile in a cold region is mainly measured through tests, long-time tests and data acquisition are needed, a large amount of complex work is brought to pile foundation design, the design process is complex, and therefore the cost is increased. There is no uniform theoretical formula describing the rheological effect of the predicted mono-pile.
Disclosure of Invention
The invention aims to provide a method for determining an empirical rheological forecast equation of a single pile in a cold region so as to provide a unified theoretical formula for describing and predicting the rheological effect of the single pile, and achieve the advantages of simplifying the design process of a frozen soil pile foundation and reducing the design cost.
In order to achieve the purpose, the invention adopts the technical scheme that:
a method for determining a cold region single-pile empirical rheological prediction equation comprises the following steps:
collecting water content and ground temperature data of a pile foundation soil sample in a pile foundation construction area;
searching the corresponding coefficient of the rheological prediction equation in an empirical rheological prediction equation coefficient list obtained by regression analysis of test data according to the water content and the ground temperature data of the soil sample and the pile body material;
and determining the cold region single-pile empirical rheological prediction equation according to the coefficient of the rheological prediction equation.
According to a preferred embodiment of the present invention, in the above empirical rheology prediction equation,
including empirical rheological equation of displacement of single pile topWherein: w is atopRepresenting the displacement of the pile top of the single pile; eta1、η2And xi1Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load; t represents time.
According to a preferred embodiment of the present invention, in the above empirical rheology prediction equation,
comprises an empirical rheological equation of single pile end sinkingWherein: w is abottomRepresenting the sinking amount of the pile end of the single pile; eta3、η4And xi2Is a rheological forecast equation coefficient, is obtained by fitting experimental data, and sigma represents the pile top load; t represents time.
According to a preferred embodiment of the present invention, in the above empirical rheology prediction equation,
including empirical rheological equations of pile tip resistance stressWherein: q. q.sbarRepresenting the resistance stress of the pile end; eta5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load; t represents time.
According to a preferred embodiment of the present invention, in the above empirical rheology prediction equation,
rheology prediction equation including mean value of pile side freezing stress
According to the preferred embodiment of the invention, the empirical rheological prediction equation is determined by using a model test of the frozen soil pile foundation.
According to a preferred embodiment of the present invention, the processing of the test data in the above model test uses a non-linear regression method.
According to the technical scheme, a unified theoretical formula is obtained by carrying out actual measurement data and empirical rheological prediction equation theoretical calculation data on the displacement of the pile top and the displacement of the pile end of the single pile to describe and predict the rheological effect of the single pile, and the aims of simplifying the design process of the frozen soil pile foundation and reducing the design cost are fulfilled.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:
FIG. 1 is a flowchart of a method for determining a cold region single-pile empirical rheological prediction equation according to an embodiment of the present invention;
FIG. 2 is a graph of the tangential stress of the pile side of the timber pile model test along the depth of the pile;
FIG. 3 is a graph showing the time-dependent change of tangential stress at the pile side of a test pile of a wood pile model;
FIG. 4 is a graph showing the time-dependent change of normal freezing stress at the pile end of a wood pile model test pile;
FIG. 5 is a graph showing the relationship between the relative displacement of the piles and the concrete and the time of the steel pipe pile;
FIG. 6 is a graph showing the relationship between unit freezing stress and time at the pile side of a timber pile, a concrete pile and a steel pipe pile;
FIG. 7 is a schematic view of a computational model of a pile;
FIG. 8 is a graph of experimental data of pile top displacement of a concrete model pile and a fitted rheological equation;
FIG. 9 is a graph of experimental data of pile bottom displacement of a concrete model pile and a fitted rheological equation;
FIG. 10 is a graph of experimental data of pile tip resistance stress of a concrete model pile and a fitted rheological equation;
FIGS. 11a to 11d are graphs showing the mean value rheological curves of frozen stress at the pile side of the concrete model pile;
FIG. 12 is a graph comparing the displacement rheological equation of the pile top of pier No. 1 of Qinghai-Tibet railway clear water river grand bridge with the measured value;
FIG. 13 is a graph comparing the pile bottom displacement rheological equation of No. 1 pier of Qinghai-Tibet railway clear water river grand bridge with the measured values;
FIG. 14 is a comparison graph of the resistance stress rheological equation of the pile end of pier No. 1 of the Qinghai-Tibet railway clear water river grand bridge and the actually measured values;
fig. 15 is a freezing stress mean value rheological equation of pile side of pier 1 of Qinghai-Tibet railway clear water river grand bridge.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
As shown in fig. 1, the method for determining the empirical rheological prediction equation of the single pile in the cold region includes the following steps:
collecting water content and ground temperature data of a pile foundation soil sample in a pile foundation construction area;
according to the water content and ground temperature data of the soil sample and the pile body material, searching the corresponding coefficient of the rheological prediction equation in an empirical rheological prediction equation coefficient list obtained by regression analysis of test data;
and determining the single-pile empirical rheological forecast equation in the cold region according to the coefficient of the rheological forecast equation.
The empirical rheological forecast equation comprises a single-pile top displacement empirical rheological equationWherein: w is atopRepresenting the displacement of the pile top of the single pile; eta1、η2And xi1Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load; t represents time.
Empirical rheological equation of single pile tip sinkingWherein: w is abottomRepresenting the sinking amount of the pile end of the single pile; eta3、η4And xi2Is a rheological forecast equation coefficient, is obtained by fitting experimental data, and sigma represents the pile top load; t represents time.
Empirical rheological equation of pile tip resistance stressWherein: q. q.sbarRepresenting the resistance stress of the pile end; eta5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load; t represents time.
Rheological forecast equation of pile side freezing stress mean value <math>
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</math> Wherein:representing the mean value of freezing stress of the single pile side; d represents the diameter of a single pile; h represents the burial depth of the pile; sigma represents the pile top load; eta5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; t represents time; γ is the pile weight. The experimental data were fit using an exponential equation in ORIGIN7.5And fitting the data such as the ground temperature in the experimental data.
And determining the empirical rheological prediction equation by using a model test of the frozen soil pile foundation, wherein a nonlinear regression method is used for processing test data in the model test.
The technical scheme utilizes the following theory:
first, similar theory
The theory of similarity is a theory for explaining the principle of similarity of various similar phenomena in nature and engineering, and the theoretical basis is three similar theories. With the similar theory as guidance, a new method for specifically researching various similar phenomena in nature and engineering, namely a 'similar method', is formed in the process of exploring natural laws.
Second, model test
Model testing is an important aspect of similar methods and generally refers to the study of phenomena using reduced or enlarged models under test conditions. The significance of the model test is as follows: firstly, the model test is used as a research means, the main parameters of a test object can be strictly controlled without being limited by external conditions and natural conditions, and the result is accurate; secondly, the model test is beneficial to highlighting the main contradiction in the complex test process, is convenient for grasping and finding the internal relation of things, and can be verified by the conclusion obtained by the prototype sometimes; third, because the size of the model is generally scaled down (scaled up only under a few special conditions, such as simulation of stress conditions of synthetic material fibers, etc.), the model is easy to manufacture, convenient to assemble and disassemble, has fewer testers, and can save money, manpower and time compared with a physical experiment; fourth, model tests can predict the performance of physical objects that have not yet been built or that cannot be directly studied at all, sometimes for exploring the fundamental performance or limit values of some phenomena or structures that are not known as much; fifth, model testing becomes the only and most important research tool for the problem of similarity of phenomena when other analytical methods are not possible.
Third, model test similarity analysis
The basic principle of the model test is to make the model have full similarity with the prototype, i.e. the similarity law of the model test. It combines all physical quantities of model test according to a certain relation to represent the actual prototype comprehensively. The method comprises the following steps:
1. the geometry is similar:
the similarity relation between the geometric similarity model and the prototype in shape, size and scale is expressed by the scale model ratio. Geometric similarity constant ClThe following were used:
wherein: l ispRepresenting the length of the prototype pile; lmRepresenting the length of the model pile; dpRepresenting the diameter of the prototype pile; dmRepresenting the model pile diameter.
After the scale model is determined, the model ratios of other physical quantities can be represented by or derived from the scale model ratios.
2. The materials are similar:
if the ratio of the modulus of elasticity of the model material to that of the prototype material isWhen the model test material is the same as the prototype material, CE1. Stress σ, similar constant of strain C in case of small deformationσ、C Are all 1; the similarity ratio of the external load P isThe similarity ratio of the displacements W is
3. The strength is similar:
the model test assumes that the dimensions of the individual cells are reduced or increased, their equilibrium conditions are unaffected while the stress concentration remains unchanged, and the stress-strain relationship is unaffected by changes in the cell dimensions and independent of the magnitude of the gradient of the stress component prior to failure, so that the strength ratio C is equal to the strength ratio C prior to failuresDetermined by the compressive strength limit of the material.
Wherein: rCP、RCMIs the compressive strength limit of prototype and model materials,CPandCMis the ultimate strain of the prototype and model materials.
4. Mechanical properties of foundation soil are similar:
if the foundation soil in the model test is the same as the field, the mechanical properties of the foundation soil are necessarily the same. Cohesion of soil in model soil CMAnd internal friction angle phiMRespectively as follows:
CM＝CσCp
ΦM＝ΦP
5. the load is similar:
according to the mutual relation between the pile side freezing force and the pile end resistance of the model test and the prototype test and the adoption of the same foundation soil for the model test and the prototype test, the similarity ratio of the vertical load and the similarity ratio of the horizontal load can be obtained as follows:
CN＝Cl 2
wherein vxIs the pile top displacement coefficient; cmIs the ratio of similarity of the foundation soil.
And fourthly, manufacturing the model pile.
The pile is used for penetrating through soft soil layers and transferring the load of an upper structure to harder or denser soil layers or bedrocks, and the length and the setting method of the pile and the working mode of the pile can be greatly changed, so that the pile can be easily adapted to different conditions and requirements of foundation engineering. The pile can be classified according to pile body material, shape of pile body and cross section, and stress condition of pile. The pile body materials are mainly divided into three types, namely a wood pile, a reinforced concrete pile and a steel pile; the pile body is divided into a column-shaped pile with equal cross section and a wedge-shaped pile according to the shape of the pile body. The cross section of the pile can be divided into a circle, a polygon, a square, a rectangle, a triangle and an H shape or an I shape; the pile tip type pile is divided into a cone type, a flaring head type and a flat bottom type. The section of the model pile body in the relevant test of the invention is circular, which belongs to a circular pile, the pile bottom is made into a flat bottom, which belongs to a flat bottom pile, and in addition, the pile body mainly comprises three materials of wood, steel and reinforced concrete.
The wooden pile is in a cylindrical form, the diameter of the pile is 3-4cm, and the length of the pile is 30-40 cm. The stake pile body both sides are processed into the recess form, scribble waterproof all-purpose adhesive after polishing with abrasive paper in the recess, treat that all-purpose adhesive begins to paste the foil gage after solidifying, paste the foil gage along stake body bilateral symmetry, and the interval is about 3-5cm, then is 2.5 m's wire and foil gage welding with length, presses 2 with second ammoniac and acetone again: 1, stirring the mixture and epoxy resin until the mixture is uniform, smearing the paste after the glue solution is thick, solidifying the glue solution after 24 hours and having high strength, and finishing the manufacturing of the whole model pile. For the thin wall of the steel pipe pile, the groove is difficult to process, so that the lead wire passes through the inside of the steel pipe, as shown in the left side of fig. 2. The reinforced concrete pile is small in size and complex in manufacturing process, two reinforcing steel bars are required to be embedded in each concrete pile, the largest particle diameter of coarse aggregate in concrete is not more than 1.2cm, medium sand with reasonable gradation is adopted as fine aggregate, and the cement is marked as No. 425.
And fourthly, a test method and a test device.
The loading mode mainly adopts three types: namely, staged loading, constant loading (i.e., the load is applied instantaneously and held constant), and continuous loading at a constant rate. According to different test purposes and requirements, the loading mode is different, for example, in order to obtain long-term freezing strength, a continuous loading mode at a constant speed is required, and the loading speed is not suitable to be too large; in order to calculate the load transfer function, hierarchical loading is required, and each level of load is applied after the displacement is stable continuously; in order to obtain the rheological equation of the relative displacement of the pile and the frozen soil, the freezing force on the pile side and the like and further analyze the influence of the rheological effect on the rheological equation, constant loading is required.
The tester mainly comprises a microcomputer-controlled electronic universal tester, a strain gauge, a displacement sensor, a notebook computer and the like.
Research on frost heaving force test of pile foundation
The frozen soil is frozen and swelled due to migration of water generated by water in the soil rising along capillaries formed by cracks and frozen pores to the freezing front. When water in soil freezes, the water in the soil not only causes severe jump change of mechanical properties of the soil, but also causes expansion deformation of a soil body, and when the pile foundation exists, the pile foundation limits deformation of frozen soil around the pile foundation, so that the contact part of the side surface and the end surface of the pile foundation and the frozen soil generates frost heaving force. Model tests show that the value of the frost heaving force is relatively large and is related to factors such as temperature, water content of soil, dry density and pile body material.
Taking a timber pile as an example, fig. 2 reveals the variation of pile-side tangential stress along the depth of the pile; fig. 3 and 4 reveal the change in pile side tangential frost heave stress and pile end normal freeze stress over time, respectively. Analysis of the test data of the model timber pile shows that the influence of the frost heaving force can be eliminated only when the sample freezing time exceeds more than 40 hours, and the mixing of the tangential frost heaving force and the freezing force is not caused.
Sixthly, pile foundation freezing force test research
The pile foundation is buried in the frozen soil, soil particles and the pile foundation are cemented together through ice crystals, and the cementing force is called the freezing strength between the pile foundation and the frozen soil. After the pile foundation bears the load, the load which begins to generate relative displacement with the frozen soil is called the ultimate freezing force; as the load increases, the freezing force gradually decreases, the displacement gradually increases and finally tends to be stable, and the load at the stable displacement is called the freezing friction force. For friction piles in permafrost areas, the freezing force is an important calculation index for determining the reasonable burial depth of pile foundations and is also a key index.
The invention adopts three model pile model tests of a wooden pile, a steel pipe pile and a concrete pile as examples to research the problem of pile foundation freezing force.
Controlling the dry density to be 1.65g/cm at the water content of 20 percent and the temperature of-5 DEG C3The length L of the steel pipe pile is 32cm, the outer diameter D is 22.2mm, the inner diameter D is 15.8mm, and the burial depth h is 26 cm; the length L of the wooden pile is 35cm, the diameter D is 31.0mm, and the buried depth h is 35 cm; the length L of the concrete pile is 65cm, the diameter D is 60mm, and the burial depth h is 60cm, and test analysis results are given for the test piece:
it can be seen from fig. 5 and 6 that when the loading time of the timber pile reaches about 40 minutes, the relative displacement of the pile and the soil changes suddenly, the unit freezing stress also reaches the maximum value at the moment, which indicates that relative slip is generated between the pile and the frozen soil, and according to the definition of the freezing force, the corresponding freezing stress is the limit freezing force q when the timber pile is loaded for 40 minutessuTaking qsu930 Kpa; the loading time of the concrete pile reaches about 22 minutes, the unit freezing stress also reaches the maximum value, which indicates that relative slippage is generated between the pile and the frozen soil, and q is takensu1000 Kpa; it can be seen from the figure that the freezing strength of the steel pipe pile is minimum, qsu690Kpa, approximately 21 minutes of time required for displacement stabilization.
Establishment of single-pile rheological prediction equation in seven-cold region
1. Pile top rheological forecast equation
According to the P-S curve of the test pile and the fitted pile body strain distribution curve along with the buried depth, the section displacement of the pile body can be calculated, and the section displacement W (z) of the pile body is the pile top displacement W (z) of the model piletopMinus pile body compression Sp(z), namely:
wherein,0the pile body strain of the pile section above the ground; (z) is the pile body strain at the burial depth z; l0Is the pile length above the ground.
Inputting data obtained by timber pile and concrete pile tests into data analysis and scientific drawing software ORIGIN7.5 for nonlinear fitting, and finding out exponential equation by selecting different equations for multiple timesThe fitting performance of experimental data is good, and the equation form is specially selected to describe the relation between the pile top displacement and the time, namely the rheological forecast equation of the pile top displacement:
wherein eta is1、η2And xi1Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load (MPa); t represents time.
2. Rheological forecast equation for pile end sinking
And (4) calculating the sinking amount of the pile end according to the p-s curve of the test pile and the compression curve of the pile body. Pile end sinking Wbottom
Pile top displacement W for model piletopMinus the total pile body compression SpNamely:
wherein,0the pile body strain of the pile section above the ground; (z) is the pile body strain at the burial depth z; l0The pile length of the part above the ground; l is the total pile length. When the cross section area of the pile body is A and the pile is equally divided into n compressible short column units, the sinking amount W of the pile endbottomCan be calculated as follows:
inputting data obtained by timber pile and concrete pile tests into data analysis and scientific drawing software ORIGIN7.5 for nonlinear fitting, and finding out exponential equation by selecting different equations for multiple timesThe fitting performance of experimental data is better, and the equation form is specially selected to describe the relation between the pile end sinking amount and the time, namely the rheological forecasting equation of the pile end sinking amount:
wherein eta is3、η4And xi2Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load (MPa); t represents time.
3. Pile tip resistance stress rheology prediction equation
Under the action of axial pressure, the pile body is axially and elastically compressed, the soil body on the pile side prevents the pile body from moving downwards to generate freezing stress on the pile side, meanwhile, the load of the pile top is transmitted to the pile bottom through the pile body, the soil layer under the pile bottom is also compressed to generate pile end resistance, and the sum of the two parts is the axial load of the pile top. Thus, the pile tip resistance stress qbarComprises the following steps:
wherein F is the vertical load of the pile top; p is the dead weight of the pile body; l0The length of the pile is the part above the ground; q. q.ss(z) is the pile side freezing force; u is the perimeter of the pile.
Resistance strain gauge type pressure cells can be buried at the pile ends, strain values read from pressure cell sensors are measured, and pile end resistance stress is directly calculated through a calibration equation.
Inputting data obtained by timber pile and concrete pile tests into data analysis and scientific drawing software ORIGIN7.5 for nonlinear fitting, and finding out exponential equation by selecting different equations for multiple timesThe fitting performance of experimental data is good, the equation form is specially selected to describe the relation between the resistance stress of the pile end and the time, and the rheological prediction equation of the resistance stress of the pile end is obtained:
wherein: q. q.sbarRepresenting the resistance stress of the pile end; eta5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load (MPa); t represents time. .
4. Mean value rheological prediction equation of pile side freezing stress and pile side freezing stress
Fig. 7 is a schematic diagram of a computational model of a pile, each pile unit is connected with the soil body by a nonlinear spring, and the pile end is also connected by a nonlinear spring, and the stress-strain relationship of the nonlinear springs is the relationship between the freezing force on the pile side and the pile displacement. Knowing that the length of the pile is L, the cross-sectional area is A, the perimeter is U, the pile top acts on a vertical load F, the pile is divided into n unit bodies which are used as compressible short columns, the length of the unit bodies is L/n, the unit body of the ith section is taken, the stress is shown in figure 7, and the unit body acts on an axial force Qi、Qi-1Gravity PiAnd pile side freezing force qs. The relation between pile side freezing force and axial force is as follows under static balance condition:
a series of measuring points are arranged along the pile side, instruments (such as a steel bar stress meter, a strain gauge and the like) are embedded, actual measurement strain can be obtained, a fitted pile body strain along pile depth distribution curve and an axial force along pile depth distribution curve can be obtained through nonlinear regression processing, and further the unit freezing force of the pile side can be obtained through numerical calculation. The change situation of the freezing stress along the depth of the pile is complex, the values of different depths are different, and the mean value of the freezing stress can reflect the load transfer situation of the pile-frozen soil system. The mean freezing force was calculated as follows:
if the length of the pile is L, the cross section area is A, the perimeter is U, the pile top acts on a vertical load F, the pile is divided into n unit bodies which are used as compressible short columns, and the length of each unit body is L/n, then:
according to the stress balance of the pile, a rheological prediction equation of the mean value of the freezing stress at the pile side can be obtained by an external load, the dead weight of the pile body and a rheological prediction equation of the resistance stress at the pile end:
wherein:representing the mean value of freezing stress of the single pile side; d represents the monopile diameter (mm); h represents the buried depth (mm) of the pile; sigma represents the pile top load (MPa); gamma is the pile weight (N/mm)3)；η5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; t represents time.
Eighthly, indoor experiment and rheological equation of reinforced concrete model test pile
Only the indoor experimental rheological measured values of concrete model test piles (pile length L is 65cm, diameter D is 6cm, and buried depth h is 60cm) at a frozen soil water content of 20% and an external load stress of 0.917MPa, 1.83MPa, 2.54MPa and 4.04MPa in a-5 ℃ environment are given (table one). The loading adopts slow static loading, and the pile top, the pile bottom displacement and the pile end resistance stress are measured after the loading is carried out for 6 hours, 12 hours, 24 hours, 2 days, 3 days … … 8 days, 10 days, 12 days and 15 days after the loading is carried out to the specified load value. The specific results of the experimental data are shown in the attached table.
The nonlinear fitted rheological equation under a load of 0.917MPa is:
table two: fitting experimental data of the concrete model test pile with the water content of 20% at the temperature of-5 ℃ to a rheological equation coefficient table;
| load(s) | η1 | η2 | η3 | η4 | η5 | η6 | ξ1 | ξ2 | ξ3 |
| 0.917MPa | -0.1428 | 0.1181 | -0.1218 | 1.2942 | 53.197 | -61.701 | 1.476 | 1.1868 | 0.8094 |
| 1.83 | -0.1758 | 0.05585 | -0.1568 | 0.05853 | 71.26 | -17.5847 | 1.098 | 1.1528 | 1.05 |
| 2.54MPa | -0.2032 | 0.03821 | -0.1892 | 0.03675 | 98.091 | -16.2087 | 1.4084 | 1.3921 | 1.135 |
| 4.04MPa | -0.2329 | 0.02238 | -0.2114 | 0.02410 | 125.32 | -15.1114 | 1.1454 | 1.4349 | 1.6455 |
Table three: the water content is 20%, and the experimental data of the concrete model test pile is fitted with a coefficient table of a rheological prediction equation under the environment of-3 ℃.
| Load(s) | η1 | η2 | η3 | η4 | η5 | η6 | ξ1 | ξ2 | ξ3 |
| 0.917MPa | -0.1445 | 0.1184 | -0.1236 | 1.2962 | 52.63 | -61.28 | 1.432 | 1.1861 | 0.8089 |
| 1.83 | -0.1783 | 0.05591 | -0.1591 | 0.05998 | 70.84 | -17.362 | 1.094 | 1.1526 | 1.044 |
| 2.54MPa | -0.2084 | 0.03828 | -0.1918 | 0.03688 | 96.37 | -16.223 | 1.4076 | 1.3908 | 1.131 |
| 4.04MPa | -0.2391 | 0.02243 | -0.2174 | 0.02463 | 122.65 | -15.016 | 1.1446 | 1.4342 | 1.642 |
Table four: the water content is 15%, and the experimental data of the concrete model test pile is fitted with a coefficient table of a rheological prediction equation under the environment of-5 ℃.
Fig. 8 to 11 are experimental values of pile top displacement, pile end resistance stress and corresponding rheological curves of the model test pile, respectively. Fig. 12 is a pile side mean freezing stress rheological curve, which is directly converted from the load stress and pile tip resistance stress rheological curves.
Ninthly, comparing theoretical calculation value of empirical rheological prediction equation with test value of construction site
The method is applied to the design of the dry bridge structure pile foundation of the perennial frozen soil section of the Qinghai-Tibet railway and the local railway in Qinghai province and woodland. In order to investigate the accuracy of a rheological forecast equation, the pile number 1 of the Qinghai-Tibet railway clear water river grand bridge is actually measured on site.
The diameter of the pile is 2m, the burial depth is 20m, the pile top load is 2881KN, and the self weight is 1708 KN. The load is converted into stress of 0.917MPa and the geometric similarity ratio ClAnd (3) setting the material and load similarity ratio to be 1, setting the time similarity coefficient to be day to month, and setting the pile top displacement and the pile bottom displacement of the No. 1 pile to be 20 times of the corresponding displacement of the experimental model pile according to the similarity theory, wherein the pile end resistance stress model experimental piles are the same. Looking up the coefficient table of the rheological equation, the rheological prediction equation under the load of 0.917MPa is as follows:
the mean value rheological equation of the frozen stress of the pile side derived from the equilibrium relation is as follows:
fig. 12 to 15 are comparison graphs of the rheological forecast equation and the measured data, and it can be known that the theoretical value of the empirical rheological forecast equation is well consistent with the measured value on site.
The technical scheme of the invention is as follows: the determination method of the rheological forecast equation is applied to the design calculation of the pile foundation in the cold region.
Finally, it should be noted that: although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (3)
1. A method for determining a cold region single-pile empirical rheological prediction equation comprises the following steps:
collecting water content and ground temperature data of a pile foundation soil sample in a pile foundation construction area;
searching the corresponding coefficient of the rheological prediction equation in an empirical rheological prediction equation coefficient list obtained by regression analysis of test data according to the water content and the ground temperature data of the soil sample and the pile body material;
determining a cold region single-pile empirical rheology prediction equation according to the coefficients of the rheology prediction equation;
the method is characterized in that the method comprises the following steps of,
in the empirical rheological prediction equation, the flow rate of the fluid is measured,
including empirical rheological equation of displacement of single pile topWherein: w is atopRepresenting the displacement of the pile top of the single pile; eta1、η2And xi1Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load; t represents time;
in the above-described empirical rheological prediction equation,
comprises an empirical rheological equation of single pile end sinkingWherein: w is abottomRepresenting the sinking amount of the pile end of the single pile; eta3、η4And xi2Is a rheological forecast equation coefficient, is obtained by fitting experimental data, and sigma represents the pile top load; t represents time;
in the above-described empirical rheological prediction equation,
including empirical rheological equations of pile tip resistance stressWherein: q. q.sbarRepresenting the resistance stress of the pile end; eta5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; sigma represents the pile top load; t represents time;
in the above-described empirical rheological prediction equation,
rheology prediction equation including mean value of pile side freezing stress
Wherein:representing the mean value of freezing stress of the single pile side; d represents the diameter of a single pile; h representsBurying depth of the pile; sigma represents the pile top load; eta5、η6And xi3Is a rheological forecast equation coefficient, and is obtained by fitting experimental data; t represents time; γ is the pile weight.
2. The method of claim 1, wherein the empirical rheological prediction equation is determined by a model test of a frozen soil pile foundation.
3. The method of claim 2, wherein the experimental data in the model experiment is processed by a non-linear regression method.
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